Fuel supply system, fuel consumption source system, and fuel supply method

Abstract

A fuel supply system (100) comprises: a fuel tank (10) that stores liquid fuel; a vaporizer (20) that vaporizes the liquid fuel into fuel gas; a pre-vaporization flow path (42) that connects the fuel tank and the vaporizer; a post-vaporization flow path (50) that connects the vaporizer and a fuel consumption source (E); a return flow path (60) that connects the post-vaporization flow path and the fuel tank; and a compressor (30) that is interposed in the return flow path, compresses the fuel gas flowing in the post-vaporization flow path, and fills the fuel tank with the compressed fuel gas.

Description

Fuel Supply System, Fuel Consumption Source System, and Fuel Supply Method 【0001】 The present disclosure relates to a fuel supply system, a fuel consumption source system, and a fuel supply method. 【0002】 Patent Document 1 discloses a supply device that vaporizes cryogenic liquefied fuel stored in a cold storage tank through a vaporizer and supplies it to an engine body. The fuel vaporized by the vaporizer can be selectively switched between the engine body and the cold storage tank as the supply destination by a switching valve. 【0003】 Japanese Patent Application Laid-Open No. 4-262044 【0004】 In Patent Document 1, depending on situations such as when the fuel consumption amount by the engine body suddenly increases or when starting the engine body, the internal pressure of the fuel tank may become insufficient, resulting in a risk of insufficient supply state. 【0005】 An aspect of the present disclosure aims to provide a fuel supply system, a fuel consumption source system, and a fuel supply method that suppress insufficient fuel supply to a fuel consumption source. 【0006】 A fuel supply system according to an aspect of the present disclosure includes a fuel tank that stores liquid fuel, a vaporizer that vaporizes the liquid fuel into fuel gas, a pre-vaporization flow path that connects the fuel tank and the vaporizer, a post-vaporization flow path that connects the vaporizer and a fuel consumption source, a return flow path that connects the post-vaporization flow path and the fuel tank, and a compressor that is interposed in the return flow path, compresses the fuel gas flowing through the post-vaporization flow path, and fills the compressed fuel gas into the fuel tank. 【0007】 FIG. 1 is a diagram showing an example of the configuration of a fuel supply system according to an exemplary embodiment. FIG. 2 is a flowchart showing an example of the operation of the fuel supply system according to the embodiment. FIG. 3 is a flowchart showing an example of the operation of the fuel supply system according to the embodiment. FIG. 4 is a diagram showing an example of the configuration of a fuel supply system according to Modification 1. FIG. 5 is a diagram showing an example of the configuration of a fuel supply system according to Modification 2. 【0008】Illustrative embodiments of the present disclosure are described below with reference to the drawings. The embodiments described below are all comprehensive or specific examples. Components in the following embodiments that are not described in the independent claim representing the highest-level concept are described as optional components. The figures in the accompanying drawings are schematic and not necessarily strictly illustrative. In each figure, substantially identical components are denoted by the same reference numerals, and redundant descriptions may be omitted or simplified. 【0009】 An exemplary fuel supply system 100 is described below. The fuel supply system 100 is a system that vaporizes liquid fuel and supplies it to a fuel consumption source E. In this embodiment, the liquid fuel is liquefied hydrogen, the fuel gas obtained by vaporizing the liquid fuel is hydrogen gas, and the fuel consumption source E is an internal combustion engine. Hereinafter, "fuel consumption source E" may be referred to as "internal combustion engine E". The internal combustion engine E consumes hydrogen gas by burning it. The internal combustion engine generates mechanical energy from the energy produced when hydrogen gas is burned. 【0010】In this embodiment, the fuel supply system 100 and the internal combustion engine E are mounted on a mobile body. The internal combustion engine E functions as the driving source for the mobile body. In this embodiment, the internal combustion engine E is a reciprocating engine that generates rotational power for the crankshaft by repeatedly burning and exploding a mixture of hydrogen gas and air supplied to the cylinder, causing the piston to reciprocate. In this embodiment, since the rotational power for the crankshaft is used as the driving output for the mobile body, the fuel consumption of the internal combustion engine E increases or decreases in order to change the output of the internal combustion engine E according to the state of the mobile body, such as the driving state. Also, by using hydrogen gas as fuel, the amount of fuel supplied to the cylinder to obtain the required output is greater compared to fossil fuels such as gasoline. Furthermore, in this embodiment, the internal combustion engine E is a direct injection engine in which hydrogen gas is directly injected into the cylinder during the compression stroke. As a result, the pressure of the hydrogen gas supplied to the fuel injector of the internal combustion engine E is set to a relatively high pressure, specifically 3 megapascals (3 MPa) or more, in order to counteract the internal pressure of the cylinder that is increased by the piston during the compression stroke. The fuel supply system 100 according to this embodiment is suitable for cases where the fuel consumption source E is an internal combustion engine, as it can supply high-pressure hydrogen gas as the fuel gas. 【0011】 Figure 1 shows an example of the configuration of a fuel supply system 100 according to an exemplary embodiment. The fuel supply system 100 of this embodiment vaporizes the stored liquid fuel and supplies the vaporized fuel to an internal combustion engine, which is a fuel consumption source E. Specifically, the fuel supply system 100 includes a fuel tank for storing liquid fuel, a vaporizer 20 for vaporizing the liquid fuel into fuel gas, a compressor 30, and a control circuit 90. The fuel tank includes one or more low-pressure fuel tanks and one or more high-pressure fuel tanks. In this embodiment, the fuel tank includes one low-pressure fuel tank 11 and two high-pressure fuel tanks 12A and 12B. The system comprising the fuel supply system 100 and the internal combustion engine E is a fuel consumption source system 1000. 【0012】The vaporizer 20 has a structure that vaporizes liquid fuel into fuel gas. Examples of the vaporizer 20 may include a heat exchanger, an electric heater, an expander, and an injection device. In this embodiment, the vaporizer 20 is a heat exchanger. The vaporizer 20 includes a structure that exchanges heat between cooling water that cools the internal combustion engine E and liquid fuel, a structure that exchanges heat between exhaust gas discharged from the internal combustion engine E and liquid fuel, a structure that exchanges heat between outside air and liquid fuel, or a combination of two or more of these. 【0013】 The fuel supply system 100 includes a pre-vaporization passage 40 connecting the fuel tank and the carburetor 20, a post-vaporization passage 50 connecting the carburetor 20 and the internal combustion engine E, and a return passage 60 connecting the post-vaporization passage 50 and the fuel tank. The pre-vaporization passage 40 includes an upstream pre-vaporization passage 41 connecting the low-pressure fuel tank 11 and the high-pressure fuel tanks 12A and 12B, and a downstream pre-vaporization passage 42 connecting the high-pressure fuel tanks 12A and 12B and the carburetor 20. 【0014】 In this embodiment, various fuel flow paths can be defined by pipes, holes through members, or passages formed between multiple members. 【0015】 The upstream pre-vaporization passage 41 includes a first upstream pre-vaporization passage 41A that connects the low-pressure fuel tank 11 and the first high-pressure fuel tank 12A, a second upstream pre-vaporization passage 41B that connects the low-pressure fuel tank 11 and the second high-pressure fuel tank 12B, and a low-pressure tank-side common passage 41C. In this embodiment, the upstream pre-vaporization passage 41 is configured to form the first upstream pre-vaporization passage 41A and the second upstream pre-vaporization passage 41B by branching into two from the low-pressure tank-side common passage 41C connected to the low-pressure fuel tank 11 and connecting to the corresponding high-pressure fuel tanks 12A and 12B, respectively. 【0016】For example, the low-pressure tank-side common passage 41C, or the upstream pre-vaporization passages 41A and 41B, may be connected to a low position such as the bottom of the low-pressure fuel tank 11 when mounted on the mobile body as a fuel supply system 100. In this embodiment, the upstream pre-vaporization passages 41A and 41B branch off from the low-pressure tank-side common passage 41C, which is connected to the low-pressure fuel tank 11, on their way to the high-pressure fuel tanks 12A and 12B, and are connected to the corresponding high-pressure fuel tanks 12A and 12B, respectively. 【0017】 The fuel supply system 100 includes upstream check valves 43A and 43B interposed in the upstream pre-vaporization passages 41A and 41B, respectively. In this embodiment, the upstream check valves 43A and 43B are located in the upstream pre-vaporization passages 41A and 41B, which are two branching portions of the upstream pre-vaporization passage 41 that branch downstream from the low-pressure tank side common passage 41C. The first upstream check valve 43A allows the flow of liquid fuel from the low-pressure fuel tank 11 toward the first high-pressure fuel tank 12A and prevents backflow of liquid fuel from the first high-pressure fuel tank 12A toward the low-pressure fuel tank 11. The second upstream check valve 43B allows the flow of liquid fuel from the low-pressure fuel tank 11 toward the second high-pressure fuel tank 12B and prevents backflow of liquid fuel from the second high-pressure fuel tank 12B toward the low-pressure fuel tank 11. The upstream check valves 43A and 43B are examples of the first check valve. 【0018】The downstream pre-vaporization passage 42 includes a first downstream pre-vaporization passage 42A that connects the vaporizer 20 and the first high-pressure fuel tank 12A, a second downstream pre-vaporization passage 42B that connects the vaporizer 20 and the second high-pressure fuel tank 12B, and a vaporizer-side confluence passage 42C. In this embodiment, the downstream pre-vaporization passage 42 is configured to form the first downstream pre-vaporization passage 42A and the second downstream pre-vaporization passage 42B by connecting to the vaporizer 20 via a vaporizer-side confluence passage 42C that merges from individual passage portions connected to the high-pressure fuel tanks 12A and 12B. The downstream pre-vaporization passages 42A and 42B may each be connected to a low position such as the bottom of the high-pressure fuel tanks 12A and 12B when mounted on a mobile body as a fuel supply system 100. In this embodiment, the downstream pre-vaporization passages 42A and 42B merge on their way from the high-pressure fuel tanks 12A and 12B to the vaporizer 20 and are connected to a single common vaporizer 20. 【0019】 The fuel supply system 100 includes downstream check valves 44A and 44B interposed in the downstream pre-vaporization flow paths 42A and 42B, respectively. Specifically, the downstream check valves 44A and 44B are located in the downstream pre-vaporization flow paths 42A and 42B, which are separate flow paths upstream of the vaporizer-side confluence flow path 42C of the downstream pre-vaporization flow path 42. The first downstream check valve 44A allows the flow of liquid fuel from the first high-pressure fuel tank 12A toward the vaporizer 20 and prevents backflow of liquid fuel from the vaporizer 20 toward the first high-pressure fuel tank 12A. The second downstream check valve 44B allows the flow of liquid fuel from the second high-pressure fuel tank 12B toward the vaporizer 20 and prevents backflow of liquid fuel from the vaporizer 20 toward the second high-pressure fuel tank 12B. The downstream check valves 44A and 44B are examples of the second check valve. 【0020】The fuel supply system 100 includes an injection pressure control valve 51 interposed in the post-vaporization flow path 50. The injection pressure control valve 51 functions as a regulator. The injection pressure control valve 51 adjusts the pressure of the fuel gas flowing from the carburetor 20 to the fuel injector of the internal combustion engine E to maintain it at a preset first set pressure P1. Specifically, the injection pressure control valve 51 opens the flow path when the pressure downstream of the injection pressure control valve 51 falls below a predetermined opening pressure due to fuel consumption, thereby increasing the pressure downstream of the injection pressure control valve 51. The injection pressure control valve 51 closes the flow path when the pressure downstream increases due to the opening of the valve and reaches a predetermined closing pressure. The closing pressure is set to a value higher than the opening pressure and lower than the pressure of the fuel gas vaporized in the carburetor 20. The injection pressure control valve 51 has the function of maintaining the downstream pressure within a predetermined range. In this way, the injection pressure control valve 51 controls the pressure of the fuel gas flowing into the internal combustion engine E, and as a result, the pressure downstream of the injection pressure control valve 51 is lower than the pressure upstream of the injection pressure control valve 51. 【0021】 In this embodiment, the opening pressure is set to a pressure at which fuel injection by the fuel injection device of the internal combustion engine E is possible. By adjusting the downstream pressure with the injection pressure control valve 51, it is possible to prevent the fuel injection pressure from being insufficient or excessive. If the pressure of the fuel gas vaporized in the vaporizer 20 is not sufficiently higher than the opening pressure, a compressor to increase the pressure may be interposed between the vaporizer 20 and the injection pressure control valve 51. This makes it possible to maintain the pressure of the fuel gas after adjustment by the injection pressure control valve 51 at the first set pressure P1. 【0022】 The injection pressure control valve 51 is an example of a control valve. In this embodiment, the injection pressure control valve 51 is a secondary pressure control valve, also called a pressure reducing valve. The injection pressure control valve 51 reduces the pressure of the fuel gas sent from the vaporizer 20 upstream of the injection pressure control valve 51, which is the primary pressure side and high pressure side, and sends the fuel gas at a stable set pressure to the post-vaporization flow path 50 downstream of the injection pressure control valve 51, which is the secondary pressure side and low pressure side. 【0023】The return passage 60 includes a first return passage 60A connecting the post-vaporization passage 50 and the first high-pressure fuel tank 12A, a second return passage 60B connecting the post-vaporization passage 50 and the second high-pressure fuel tank 12B, and a carburetor-side common passage 60C. In this embodiment, the return passage 60 is formed by branching into two from the carburetor-side common passage 60C connected to the post-vaporization passage 50 and connecting to the corresponding high-pressure fuel tanks 12A and 12B, respectively, thereby forming the first return passage 60A and the second return passage 60B. In this embodiment, the carburetor-side common passage 60C is connected to the portion of the post-vaporization passage 50 downstream of the injection pressure control valve 51. For example, the return passages 60A and 60B may each be connected to a high position such as the top of the corresponding high-pressure fuel tanks 12A and 12B when mounted on a mobile body as a fuel supply system 100. 【0024】 The compressor 30 is interposed in the return flow path 60. In this embodiment, the compressor 30 is interposed in the vaporizer-side common flow path 60C of the return flow path 60. Alternatively, the compressor 30 may be interposed in the return flow paths 60A and 60B after branching off from the vaporizer-side common flow path 60C. 【0025】 The compressor 30 compresses the fuel gas flowing through the post-vaporization passage 50 to increase its pressure, and fills the fuel tanks with the pressurized fuel gas. Specifically, the compressor 30 fills the high-pressure fuel tanks 12A and 12B with the pressurized fuel gas. The compressor 30 draws in the fuel gas flowing in from the post-vaporization passage 50, compresses it, and discharges the pressurized fuel gas from the return passage 60 into the vaporizer-side common passage 60C. The fuel gas discharged successively from the compressor 30 reaches the high-pressure fuel tanks 12A and 12B via the return passages 60A and 60B, which are the downstream branching sections of the return passage 60. Inside the high-pressure fuel tanks 12A and 12B, the pressurized fuel gas presses against the liquid fuel surface. The liquid fuel in the high-pressure fuel tanks 12A and 12B is not pushed out into the upstream pre-vaporization passages 41A and 41B by the action of the upstream check valves 43A and 43B, but is pushed out into the downstream pre-vaporization passages 42A and 42B. 【0026】The compressor 30 can be any known compressor, as long as it has a structure that inhales and compresses fuel gas and discharges it to the outside of the compressor 30. In this embodiment, since the temperature of the fuel gas inhaled into the compressor 30 is in a low-temperature region well below zero degrees Celsius, it is desirable that the compressor 30 has a structure that can inhale and compress fuel gas in such a low-temperature region. The compressor 30 may have a compression structure that compresses the fuel gas by the rotational motion of an impeller or rotor, or a compression structure that compresses the fuel gas by the reciprocating motion of a piston. In this embodiment, the compressor 30 is an electric compressor that includes a compression structure and an electric actuator that drives the compression structure. 【0027】 The fuel supply system 100 includes a compressor pressure control valve 31 interposed in the vaporizer-side common flow path 60C within the return flow path 60. The compressor pressure control valve 31 is interposed in a bypass flow path 60Ca that bypasses the compressor 30 by connecting the upstream and downstream flow paths of the compressor 30. In this embodiment, the upstream and downstream ends of the bypass flow path 60Ca are connected to the vaporizer-side common flow path 60C. 【0028】 The compressor pressure control valve 31 adjusts the pressure of the fuel gas flowing from the compressor 30 to the high-pressure fuel tanks 12A and 12B to maintain it at a preset second set pressure P2. The second set pressure P2 is set higher than the first set pressure P1. The second set pressure P2 is such that the fuel gas at the second set pressure P2 can push the liquid fuel in the high-pressure fuel tanks 12A and 12B out of the flow path 42A and 42B to the downstream pre-vaporization passages 42A and 42B, against the first set pressure P1. 【0029】 In this embodiment, the compressor pressure control valve 31 is a primary pressure control valve, also called a relief valve. The compressor pressure control valve 31 closes the bypass passage 60Ca when the pressure of the fuel gas downstream of the compressor 30, which is the primary side, that is, the pressure of the fuel gas in the return passages 60A and 60B, which are branching parts of the return passage 60, is less than or equal to the second set pressure P2. The compressor pressure control valve 31 opens the bypass passage 60Ca when the pressure of the fuel gas on the primary side exceeds the second set pressure P2, and releases the pressure exceeding the second set pressure P2 to the upstream side of the compressor 30, which is the secondary side. 【0030】The fuel supply system 100 includes a gas filling passage 70. In this embodiment, the gas filling passage 70 connects the vaporizer-side common passage 60C of the return passage 60 to the low-pressure fuel tank 11. The gas filling passage 70 supplies filling gas at a pressure lower than the pressure of the fuel gas supplied to the high-pressure fuel tanks 12A and 12B to the low-pressure fuel tank 11. The gas filling passage 70 connects the portion of the return passage 60 downstream of the compressor 30 in the direction of fuel gas flow to the low-pressure fuel tank 11. When the system is mounted on a mobile body as a fuel supply system, the gas filling passage 70 may be connected to a high position such as the top of the low-pressure fuel tank 11. 【0031】 The fuel supply system 100 includes a gas filling pressure control valve 71 interposed in the gas filling passage 70. The gas filling pressure control valve 71 is interposed in the gas filling passage 70 downstream of the compressor 30 in the direction of fuel gas flow. The gas filling pressure control valve 71 adjusts the pressure of the fuel gas flowing from the compressor 30 to the low-pressure fuel tank 11 to maintain it at a preset third set pressure P3. The third set pressure P3 is set lower than the second set pressure P2. The third set pressure P3 is set higher than atmospheric pressure. Preferably, the third set pressure P3 is at least twice atmospheric pressure, and more preferably at least three times atmospheric pressure. 【0032】 In this embodiment, the gas filling pressure control valve 71 is a secondary pressure control valve, also called a pressure reducing valve, similar to the injection pressure control valve 51. The gas filling pressure control valve 71 reduces the pressure of the fuel gas sent from upstream of the gas filling pressure control valve 71, which is on the primary pressure side and high pressure side, in the gas filling passage 70, and sends the fuel gas downstream of the gas filling pressure control valve 71, which is on the secondary pressure side and low pressure side, at a stable set pressure. The gas filling pressure control valve 71 is one example of a filling pressure reducing valve. 【0033】The fuel supply system 100 includes a safety valve 11a in the low-pressure fuel tank 11. The safety valve 11a is connected to the low-pressure fuel tank 11. Alternatively, the safety valve 11a is connected to a discharge passage 11b extending from the low-pressure fuel tank 11. In this embodiment, the safety valve 11a is connected to the discharge passage 11b. The discharge passage 11b is connected to the low-pressure fuel tank 11 and discharges the fuel gas in the low-pressure fuel tank 11 to the outside. The safety valve 11a maintains the internal pressure of the low-pressure fuel tank 11 at or below a preset fourth set pressure P4. The fourth set pressure P4 may be set from a range greater than the third set pressure P3 and less than or equal to the pressure resistance of the low-pressure fuel tank 11. In this embodiment, the safety valve 11a is a relief valve that releases pressure exceeding the fourth set pressure P4, releasing the pressure inside the low-pressure fuel tank 11 to the outside. The safety valve 11a may also be a primary pressure control valve, similar to the compressor pressure control valve 31. 【0034】 The fuel supply system 100 includes a gas filling switching valve 61 interposed in the return passage 60. The gas filling switching valve 61 has a structure that switches between the high-pressure side fuel tanks 12A and 12B to which the fuel gas compressed by the compressor 30 should be supplied. In this embodiment, the gas filling switching valve 61 includes a first switching valve 61A interposed in the first return passage 60A and a second switching valve 61B interposed in the second return passage 60B. The first switching valve 61A communicates with the first high-pressure side fuel tank 12A, and the second switching valve 61B communicates with the second high-pressure side fuel tank 12B. 【0035】 The first switching valve 61A is an on / off control valve that operates to open and close the first return passage 60A. The second switching valve 61B is an on / off control valve that operates to open and close the second return passage 60B. The operation of the two switching valves 61A and 61B switches between the high-pressure fuel tank 12A or 12B to which the fuel gas should be supplied. The switching valves 61, 61A, and 61B are solenoid valves and their operation is controlled by the control circuit 90. 【0036】The fuel supply system 100 includes a first discharge passage 12Aa and a first on / off control valve 12Ab interposed in the first discharge passage 12Aa, connected to the first high-pressure fuel tank 12A. The first discharge passage 12Aa is connected to the first high-pressure fuel tank 12A and discharges fuel gas from within the first high-pressure fuel tank 12A. The first on / off control valve 12Ab communicates with the first high-pressure fuel tank 12A. The first on / off control valve 12Ab operates to open and close the first discharge passage 12Aa. The first on / off control valve 12Ab is a solenoid valve and its operation is controlled by the control circuit 90. In this embodiment, the first discharge passage 12Aa discharges fuel gas from within the first high-pressure fuel tank 12A to the outside. The first discharge passage 12Aa may be connected to a high position, such as the top, of the first high-pressure fuel tank 12A when the fuel supply system 100 is mounted on a mobile body. 【0037】 The fuel supply system 100 includes a second discharge passage 12Ba and a second on / off control valve 12Bb interposed in the second discharge passage 12Ba, connected to the second high-pressure fuel tank 12B. The second discharge passage 12Ba is connected to the second high-pressure fuel tank 12B and discharges fuel gas from within the second high-pressure fuel tank 12B. The second on / off control valve 12Bb communicates with the second high-pressure fuel tank 12B. The second on / off control valve 12Bb operates to open and close the second discharge passage 12Ba. The second on / off control valve 12Bb is a solenoid valve and its operation is controlled by the control circuit 90. In this embodiment, the second discharge passage 12Ba discharges fuel gas from within the second high-pressure fuel tank 12B to the outside. The second discharge passage 12Ba may be connected to a high position, such as the top, of the second high-pressure fuel tank 12B when the fuel supply system 100 is mounted on a mobile body. The on / off control valves 12Ab and 12Bb are examples of gas discharge valves. 【0038】The discharge passages 12Aa and 12Ba may be connected to a low-pressure fuel tank 11 and configured to discharge fuel gas to the low-pressure fuel tank 11. The discharge passages 12Aa and 12Ba may also be connected to a buffer tank for temporarily storing fuel gas and configured to discharge fuel gas to the buffer tank. For example, the fuel gas in the buffer tank may be pressurized and reused. The pressurized fuel gas may be supplied to a position downstream of the injection pressure control valve 51 in the post-vaporization passage 50. The pressurized fuel gas may also be supplied to a position upstream of the compressor 30 in the return passage 60. 【0039】 In this embodiment, the high-pressure fuel tanks 12A and 12B have the same structure. The size, shape, and performance of the high-pressure fuel tanks 12A and 12B are the same. 【0040】 Each fuel tank 11, 12A, and 12B is airtight. The low-pressure fuel tank 11 is used to store liquefied hydrogen, which is a liquid fuel. The low-pressure fuel tank 11 has a heat-insulating structure to prevent the temperature of the liquefied hydrogen from rising. Each high-pressure fuel tank 12A and 12B is used to temporarily store fuel in order to supply fuel to the internal combustion engine E. Each high-pressure fuel tank 12A and 12B supplies liquid fuel downstream at a higher pressure than the low-pressure fuel tank 11. Therefore, the internal pressure in each high-pressure fuel tank 12A and 12B is greater than the internal pressure in the low-pressure fuel tank 11. Each high-pressure fuel tank 12A and 12B has higher pressure resistance than the low-pressure fuel tank 11. For example, the pressure resistance of each high-pressure fuel tank 12A and 12B is preferably 10 times or more, and more preferably 20 times or more, than the pressure resistance of the low-pressure fuel tank 11. The pressure resistance of the low-pressure fuel tank 11 is preferably three times or more the atmospheric pressure, and more preferably five times or more the atmospheric pressure. 【0041】It is preferable that the internal pressure increase in each high-pressure fuel tank 12A, 12B is faster and easier than the internal pressure increase in the low-pressure fuel tank 11. For this reason, the liquid fuel capacity of each high-pressure fuel tank 12A, 12B is smaller than the liquid fuel capacity of the low-pressure fuel tank 11. The liquid fuel capacity of the low-pressure fuel tank 11 is such that it can accommodate the maximum amount of liquid fuel that has been set in advance for the mobile unit. The liquid fuel capacity of each high-pressure fuel tank 12A, 12B is such that it can accommodate the amount of liquid fuel that the fuel consumption source E may need for operation over a set period of time. In this embodiment, the capacity of each high-pressure fuel tank 12A, 12B is 1 liter. 【0042】 The low-pressure fuel tank 11 needs to maintain the large amount of liquid fuel stored in it in a liquid state. For this reason, the heat retention of the low-pressure fuel tank 11 is higher than that of the high-pressure fuel tanks 12A and 12B. For example, the low-pressure fuel tank 11 may have an outer shell made of a material with lower thermal conductivity than the high-pressure fuel tanks 12A and 12B, or it may be covered with a material with low thermal conductivity. 【0043】 In both the low-pressure fuel tank 11 and the high-pressure fuel tanks 12A and 12B, the liquid fuel outlet is preferably located at the bottom of the tank. Examples of liquid fuel outlets include the connection between the low-pressure fuel tank 11 and the low-pressure tank-side common passage 41C, the connection between the first high-pressure fuel tank 12A and the first downstream pre-vaporization passage 42A, and the connection between the second high-pressure fuel tank 12B and the second downstream pre-vaporization passage 42B. In other words, the connection between the low-pressure fuel tank 11 and the low-pressure tank-side common passage 41C is preferably located at the bottom of the low-pressure fuel tank 11. The connection between the first high-pressure fuel tank 12A and the first downstream pre-vaporization passage 42A is preferably located at the bottom of the first high-pressure fuel tank 12A. The connection between the second high-pressure fuel tank 12B and the second downstream pre-vaporization passage 42B is preferably located at the bottom of the second high-pressure fuel tank 12B. 【0044】In any of the high-pressure side fuel tanks 12A and 12B, the inlet of the liquid fuel is preferably located above the outlet of the liquid fuel. Examples of the inlet of the liquid fuel include the connection portions between the first high-pressure side fuel tank 12A and the first upstream pre-vaporization flow path 41A, and between the second high-pressure side fuel tank 12B and the second upstream pre-vaporization flow path 41B. In other words, the connection portion between the first high-pressure side fuel tank 12A and the first upstream pre-vaporization flow path 41A is preferably located above the connection portion between the first high-pressure side fuel tank 12A and the first downstream pre-vaporization flow path 42A. The connection portion between the second high-pressure side fuel tank 12B and the second upstream pre-vaporization flow path 41B is preferably located above the connection portion between the second high-pressure side fuel tank 12B and the second downstream pre-vaporization flow path 42B. 【0045】 In any of the low-pressure side fuel tank 11 and the high-pressure side fuel tanks 12A and 12B, the inlet of the fuel gas is preferably located at the upper part of the tank. In particular, in any of the high-pressure side fuel tanks 12A and 12B, the inlet of the fuel gas is preferably located above the inlet and outlet of the liquid fuel. Examples of the inlet of the fuel gas include the connection portion between the low-pressure side fuel tank 11 and the gas filling flow path 70, the connection portion between the first high-pressure side fuel tank 12A and the first return flow path 60A, and the connection portion between the second high-pressure side fuel tank 12B and the second return flow path 60B. In other words, the connection portion between the low-pressure side fuel tank 11 and the gas filling flow path 70 is preferably located above the connection portion between the low-pressure side fuel tank 11 and the low-pressure tank side common flow path 41C. The connection portion between the first high-pressure side fuel tank 12A and the first return flow path 60A is preferably located above the connection portion between the first high-pressure side fuel tank 12A and the first upstream pre-vaporization flow path 41A. The connection portion between the second high-pressure side fuel tank 12B and the second return flow path 60B is preferably located above the connection portion between the second high-pressure side fuel tank 12B and the second upstream pre-vaporization flow path 41B. 【0046】 By positioning the inlet of the liquid fuel, the outlet of the liquid fuel, and the inlet of the fuel gas as described above, it is possible to prevent the fuel gas from mixing into the liquid fuel discharged from the low-pressure side fuel tank 11 and the high-pressure side fuel tanks 12A and 12B. That is, it is possible to prevent the fuel gas from mixing into the flow path through which the liquid fuel flows. 【0047】 The fuel supply system 100 includes various sensors. The fuel supply system 100 may include one or more of a temperature sensor that detects the internal temperature, a pressure sensor that detects the internal pressure, and a liquid level sensor that detects the position of the liquid fuel level in each of the fuel tanks 11, 12A, and 12B. In the present embodiment, the fuel supply system 100 includes all of the above sensors. Each sensor sends the detection result to the control circuit 90. 【0048】 The fuel supply system 100 may be provided with sensors for detecting the state of the fluid in the flow path. For example, the fuel supply system 100 may include pressure sensors for detecting the pressure of the fuel gas at the upstream and downstream positions of the switching valves 61A and 61B in each of the return flow paths 60A and 60B, respectively. Such sensors for detecting the state of the fluid send the detection result to the control circuit 90. 【0049】 The control circuit 90 includes one or more processors P such as a CPU (Central Processing Unit) or a DSP (Digital Signal Processor), and a memory M. The control circuit 90 includes one or more processing circuits, and the processor P and the memory M function as components of the processing circuit. The control circuit 90 may be included in an electronic control unit that controls the moving body, or may be a circuit separate from the electronic control unit. 【0050】 The memory M may include one or more memories, one or more storages, or both of these. Examples of the memory may include semiconductor memories. Examples of the storage may include semiconductor memories, hard disk drives (HDDs), and solid state drives (SSDs). Examples of the semiconductor memory may include volatile memories such as RAM (Random Access Memory), and non-volatile memories such as ROM (Read-Only Memory). 【0051】Some or all of the functions of the control circuit 90 may be realized by the CPU, as a processor P, executing a program recorded in ROM using RAM, as a memory M, as working memory. Some or all of the functions of the control circuit 90 may be realized by dedicated hardware circuits such as electronic circuits or integrated circuits. Some or all of the functions of the control circuit 90 may be realized by a combination of the above-mentioned software functions and hardware circuits. The multiple processes of this disclosure may be realized by one processing circuit of the control circuit 90, or by the cooperation of multiple processing circuits of the control circuit 90. 【0052】 The control circuit 90 acquires detection results from various sensors and controls the operation of various valves based on the acquired detection results. For example, the control circuit 90 controls the operation of each switching valve 61A, 61B and each on / off control valve 12Ab, 12Bb. The control circuit 90 controls the operation of the compressor 30, including starting, stopping, and operating speed. 【0053】 One operation of the fuel supply system 100 according to the embodiment will be described. Figures 2 and 3 are flowcharts showing an example of the operation of the fuel supply system 100 according to the embodiment. This example shows the operation of fuel supply control by the control circuit 90 from before the preparation for operation of the internal combustion engine E to during operation. 【0054】 As shown in Figures 2 and 3, in step S101, the control circuit 90 receives a start preparation command that instructs the start of preparations for starting the internal combustion engine E. For example, when the ignition power or accessory power of the mobile body on which the fuel supply system 100 is installed is turned ON from the OFF state, the electronic control unit of the mobile body may transmit a start preparation command to the control circuit 90. 【0055】 In step S102, the control circuit 90 starts fuel supply control. 【0056】 In the start-up standby state before receiving a start-up preparation command, power is supplied to the control circuit 90. Furthermore, the fuel supply system 100 is in its initial state, in which liquefied hydrogen is stored in the low-pressure fuel tank 11, the switching valves 61A and 61B are in the closed state, and the on / off control valves 12Ab and 12Bb are in the closed state. 【0057】 The control circuit 90, while waiting for the internal combustion engine E to start, executes a start preparation process including steps S103 to S112. 【0058】 In step S103, the control circuit 90 performs a remaining fuel check process to confirm the remaining amount of liquefied hydrogen in each high-pressure fuel tank 12A, 12B. Specifically, the control circuit 90 determines whether the remaining amount of liquefied hydrogen in each high-pressure fuel tank 12A, 12B is less than a preset remaining amount threshold, based on the detection results of the liquid level sensors in each high-pressure fuel tank 12A, 12B. If the remaining amount of liquefied hydrogen in at least one of the high-pressure fuel tanks 12A, 12B is less than the remaining amount threshold (Yes in step S103), the control circuit 90 proceeds to step S104. If the remaining amount of liquefied hydrogen in all of the high-pressure fuel tanks 12A, 12B is greater than or equal to the remaining amount threshold (No in step S103), the control circuit 90 proceeds to step S105. 【0059】 In steps S104 and S106, the control circuit 90 performs residual gas discharge processing to discharge hydrogen gas from the high-pressure fuel tanks 12A and 12B. In step S104, the control circuit 90 determines that the high-pressure fuel tanks 12A and 12B, in which the remaining amount of liquefied hydrogen is below the remaining amount threshold, are the high-pressure fuel tanks into which liquefied hydrogen should be introduced. The control circuit 90 operates the on / off control valves 12Ab and 12Bb corresponding to the high-pressure fuel tanks 12A and 12B into which liquefied hydrogen should be introduced, from the closed state to the open state. 【0060】 In step S106, the control circuit 90 determines, based on the detection results of the pressure sensors in the high-pressure fuel tanks 12A and 12B into which liquefied hydrogen should be introduced, that the internal pressure of the high-pressure fuel tanks 12A and 12B has fallen below the third set pressure P3, and operates the open-off control valves 12Ab and 12Bb to the closed position. 【0061】Next, in steps S107 and S108, the control circuit 90 performs preparation processing to prepare for the supply of liquefied hydrogen from the low-pressure fuel tank 11. In step S107, the control circuit 90 determines whether the internal pressure of the low-pressure fuel tank 11 is less than the third set pressure P3 based on the detection result of the pressure sensor of the low-pressure fuel tank 11. If the internal pressure of the low-pressure fuel tank 11 is less than the third set pressure P3 (Yes in step S107), the control circuit 90 proceeds to step S108. If the internal pressure is equal to or greater than the third set pressure P3 (No in step S107), the control circuit 90 proceeds to step S109. 【0062】 In step S108, the control circuit 90 starts the compressor 30. As a result, hydrogen gas pressurized by the compressor 30 is supplied to the low-pressure fuel tank 11, and the internal pressure of the low-pressure fuel tank 11 increases. Therefore, the control circuit 90 can fill the low-pressure fuel tank 11 with hydrogen gas by operating the compressor 30. When the control circuit 90 determines that the internal pressure of the low-pressure fuel tank 11 has reached the third set pressure P3, it stops the compressor 30 and proceeds to step S109. The control circuit 90 may also proceed to step S109 without stopping the compressor 30. Note that since the third set pressure P3 is set to a low pressure as described above, the internal pressure of the low-pressure fuel tank 11 can reach the third set pressure P3 in a relatively short time by the operation of the compressor 30. Since the time required for the internal pressure of the low-pressure fuel tank 11 to reach the third set pressure P3 can be shortened, the responsiveness of the internal pressure of the low-pressure fuel tank 11 to the operation of the compressor 30 can be improved. 【0063】In step S109, the control circuit 90 executes a fuel introduction process to introduce liquefied hydrogen into the high-pressure fuel tanks 12A and 12B into which liquefied hydrogen should be introduced. Because the internal pressure of the low-pressure fuel tank 11 is higher than the internal pressure of the high-pressure fuel tanks 12A and 12B into which liquefied hydrogen should be introduced, the pressure difference between the two causes liquefied hydrogen to flow from the low-pressure fuel tank 11 into the high-pressure fuel tanks 12A and 12B. The inflow of liquefied hydrogen can continue until the pressure difference becomes zero. Therefore, the control circuit 90 can push the liquefied hydrogen in the low-pressure fuel tank 11 towards the high-pressure fuel tanks 12A and 12B by filling the low-pressure fuel tank 11 with hydrogen gas. 【0064】 The control circuit 90 determines, based on the detection results of the liquid level sensors in the high-pressure fuel tanks 12A and 12B into which liquefied hydrogen should be introduced, whether the remaining amount of liquefied hydrogen in the high-pressure fuel tanks 12A and 12B is equal to or greater than the remaining amount threshold. If the remaining amount is equal to or greater than the remaining amount threshold (Yes in step S109), the control circuit 90 proceeds to step S105. If the remaining amount is less than the remaining amount threshold (No in step S109), the control circuit 90 returns to step S104. 【0065】 In steps S105 and S110, the control circuit 90 performs an internal pressure check process to confirm the internal pressure of the high-pressure fuel tanks 12A and 12B. In step S105, the control circuit 90 determines which high-pressure fuel tank 12A or 12B will supply liquefied hydrogen to the internal combustion engine E according to a predetermined priority rule. Hereafter, the high-pressure fuel tank 12A or 12B from which the supply of liquefied hydrogen has been determined in this step will be referred to as "high-pressure fuel tank 12C", the high-pressure fuel tank that does not supply liquefied hydrogen will be referred to as "high-pressure fuel tank 12D", the switching valve corresponding to high-pressure fuel tank 12C will be referred to as "switching valve 61C", and the switching valve corresponding to high-pressure fuel tank 12D will be referred to as "switching valve 61D". Examples of priority rules may include a rule that the high-pressure fuel tank with the largest remaining amount of liquefied hydrogen will supply the liquefied hydrogen, and a rule that the high-pressure fuel tank whose remaining amount of liquefied hydrogen is equal to or greater than the remaining amount threshold in step S103 will supply the liquefied hydrogen. 【0066】In step S110, the control circuit 90 determines whether the internal pressure of the high-pressure fuel tank 12C is less than the second set pressure P2, based on the detection result of the pressure sensor of the high-pressure fuel tank 12C determined in step S105. If the internal pressure is less than the second set pressure P2 (Yes in step S110), the control circuit 90 proceeds to step S111. If the internal pressure is equal to or greater than the second set pressure P2 (No in step S110), the control circuit 90 proceeds to step S113. 【0067】 In steps S111 and S112, the control circuit 90 performs a filling process to fill the high-pressure fuel tank 12C, which has an internal pressure less than the second set pressure P2, with hydrogen gas. In step S111, the control circuit 90 operates the switching valve 61C corresponding to the high-pressure fuel tank 12C, which has an internal pressure less than the second set pressure P2, from a closed state to an open state. If the compressor 30 is running, the control circuit 90 continues to operate, and if the compressor 30 is stopped, it starts the compressor 30. 【0068】 Therefore, the control circuit 90 operates the compressor 30 and moves the switching valve 61C corresponding to the high-pressure fuel tank 12C from a closed state to an open state, thereby filling the high-pressure fuel tank 12C with hydrogen gas. Furthermore, the liquid fuel capacity of the high-pressure fuel tank 12C is smaller than that of the low-pressure fuel tank 11, for example, a small capacity such as 1 liter. For this reason, the internal pressure of the high-pressure fuel tank 12C can reach the second set pressure P2 in a relatively short time by the operation of the compressor 30. Since the time required for the internal pressure of the high-pressure fuel tank 12C to reach the second set pressure P2 can be shortened, the responsiveness of the internal pressure of the high-pressure fuel tank 12C to the operation of the compressor 30 can be improved. 【0069】 In step S112, the control circuit 90 determines whether the internal pressure of the high-pressure fuel tank 12C has reached the second set pressure P2, based on the detection result of the pressure sensor of the high-pressure fuel tank 12C, which has an internal pressure less than the second set pressure P2. If the internal pressure is equal to or greater than the second set pressure P2 (Yes in step S112), the control circuit 90 proceeds to step S113. If the internal pressure is less than the second set pressure P2 (No in step S112), the control circuit 90 repeats step S112. 【0070】 In step S113, the control circuit 90 performs a notification process to notify that the internal combustion engine E is ready to start. For example, the control circuit 90 may transmit a signal to the electronic control unit of the mobile vehicle equipped with the fuel supply system 100 indicating that the vehicle is ready to start. The electronic control unit may display an indication on a display or indicator light on the mobile vehicle that the vehicle is ready to start. This allows the driver of the mobile vehicle to perceive that the vehicle is ready to start. 【0071】 Next, in steps S114 to S124, the control circuit 90 performs operation processing to operate the internal combustion engine E. First, in steps S114 to S116, the control circuit 90 performs supply processing to control the fuel supply to the internal combustion engine E. In step S114, the control circuit 90 receives a command to start the internal combustion engine E, input by the driver, via the electronic control unit. For example, the driver inputs a command to start the internal combustion engine E via an input device such as a start button on the vehicle. 【0072】 In step S115, the control circuit 90 controls the operation of the compressor 30 to maintain the hydrogen gas pressure, which is the pressure of the hydrogen gas supplied to the internal combustion engine E and has been adjusted by the injection pressure control valve 51, at a first set pressure P1. As the internal combustion engine E consumes hydrogen gas, the injection pressure control valve 51 repeatedly operates intermittently between an open state and a closed state. This can cause the internal pressure of the high-pressure fuel tank 12C, which was determined in step S105 and is discharging liquefied hydrogen, to decrease. The control circuit 90 controls the operation of the compressor 30 to increase or decrease the discharge amount of the compressor 30 in accordance with the increase or decrease in the amount of hydrogen gas consumed by the internal combustion engine E. In this way, the control circuit 90 prevents a decrease in the internal pressure of the high-pressure fuel tank 12C, which is discharging liquefied hydrogen, and maintains the hydrogen gas injection pressure adjusted by the injection pressure control valve 51. The control circuit 90 may obtain information on the amount of hydrogen gas consumed by the internal combustion engine E from the electronic control unit. 【0073】Therefore, the control circuit 90 operates the compressor 30 while maintaining the state of the switching valve 61C corresponding to the high-pressure fuel tank 12C in an open state, thereby filling the high-pressure fuel tank 12C with hydrogen gas and pushing the liquefied hydrogen in the high-pressure fuel tank 12C toward the internal combustion engine E with the hydrogen gas. In the fuel supply system 100, liquefied hydrogen flows from the low-pressure fuel tank 11 through the high-pressure fuel tank 12C toward the vaporizer 20. In the direction of flow of liquefied hydrogen, the pressure of the liquefied hydrogen decreases as it moves upstream. For example, the pressure of liquefied hydrogen in the vaporizer-side merging passage 42C is higher than the pressure of liquefied hydrogen in the high-pressure fuel tank 12C, and the pressure of liquefied hydrogen in the high-pressure fuel tank 12C is higher than the pressure of liquefied hydrogen in the low-pressure fuel tank 11 and the low-pressure tank-side common passage 41C. The downstream check valves 44A and 44B are interposed in the downstream pre-vaporization passages 42A and 42B to prevent backflow of liquefied hydrogen from the vaporizer 20 toward the high-pressure fuel tank 12C. The upstream check valves 43A and 43B are interposed in the upstream pre-vaporization passages 41A and 41B to prevent backflow of liquefied hydrogen from the high-pressure fuel tank 12C toward the low-pressure fuel tank 11. 【0074】 In step S116, the control circuit 90 determines whether the remaining amount of liquefied hydrogen in the high-pressure fuel tank 12C from which liquefied hydrogen is being discharged is less than the remaining amount threshold. If the remaining amount is less than the remaining amount threshold (Yes in step S116), the control circuit 90 proceeds to step S117. If the remaining amount is equal to or greater than the remaining amount threshold (No in step S116), the control circuit 90 repeats step S115. 【0075】 In steps S117 to S124, the control circuit 90 performs a switching process to switch the high-pressure fuel tank 12C that supplies liquefied hydrogen to the internal combustion engine E to another high-pressure fuel tank 12D. In step S117, the control circuit 90 determines that the other high-pressure fuel tank 12D, which does not supply liquefied hydrogen to the internal combustion engine E and whose remaining amount of liquefied hydrogen is above a threshold, is the high-pressure fuel tank from which the liquefied hydrogen should be discharged. 【0076】In step S118, the control circuit 90 operates the switching valve 61C corresponding to the high-pressure fuel tank 12C from the open state to the closed state, and operates the switching valve 61D corresponding to the high-pressure fuel tank 12D from the closed state to the open state. 【0077】 In step S119, the control circuit 90 controls the operation of the compressor 30 to maintain the pressure of the hydrogen gas adjusted by the injection pressure control valve 51 at the first set pressure P1, similar to step S115. 【0078】 In step S120, the control circuit 90 determines that the high-pressure fuel tank 12C, which has a remaining amount of liquefied hydrogen below the remaining amount threshold, is the high-pressure fuel tank into which liquefied hydrogen should be introduced. 【0079】 In step S121, the control circuit 90 operates the on / off control valves 12Ab and 12Bb corresponding to the high-pressure fuel tank 12C from the closed state to the open state, similar to step S104. 【0080】 In step S122, the control circuit 90, similar to step S106, determines, based on the detection result of the pressure sensor of the high-pressure fuel tank 12C, that the internal pressure of the high-pressure fuel tank 12C has fallen below the third set pressure P3, and operates the on / off control valves 12Ab and 12Bb corresponding to the high-pressure fuel tank 12C from the open state to the closed state. 【0081】 In step S123, since the compressor 30 is operating, the internal pressure of the low-pressure fuel tank 11 can be maintained at the third set pressure P3. As a result, liquefied hydrogen flows from the low-pressure fuel tank 11 to the high-pressure fuel tank 12C due to the pressure difference between the internal pressure of the low-pressure fuel tank 11 and the internal pressure of the high-pressure fuel tank 12C. The inflow of liquefied hydrogen can continue until the pressure difference becomes zero. 【0082】 The control circuit 90 determines, based on the detection result of the liquid level sensor in the high-pressure fuel tank 12C, whether the remaining amount of liquefied hydrogen in the high-pressure fuel tank 12C is equal to or greater than the remaining amount threshold. If the remaining amount is equal to or greater than the remaining amount threshold (Yes in step S123), the control circuit 90 proceeds to step S124. If the remaining amount is less than the remaining amount threshold (No in step S123), the control circuit 90 returns to step S121. 【0083】 In step S124, the control circuit 90 proceeds to step S125 if it receives a stop command to stop the operation of the internal combustion engine E (Yes in step S124), and to step S115 if it has not received a stop command (No in step S124). For example, a command to stop the operation of the internal combustion engine E is input by the driver to the input device of the mobile body, and the electronic control unit transmits a stop command in accordance with that command to the control circuit 90. When the control circuit 90 proceeds to step S115, it replaces the high-pressure fuel tank 12C in steps S115 to S123 with the high-pressure fuel tank 12D, and replaces the high-pressure fuel tank 12D in steps S115 to S123 with the high-pressure fuel tank 12C, and executes the control. 【0084】 In step S125, the control circuit 90 terminates fuel supply control. Accordingly, the control circuit 90 stops the internal combustion engine E, operates the switching valves 61A and 61B to the closed position, and operates the on / off control valves 12Ab and 12Bb to the closed position. 【0085】 In steps S101 to S113, the control circuit 90 performs the preparation for starting the internal combustion engine E. In the preparation for starting, the control circuit 90 adjusts the remaining amount of liquefied hydrogen in each of the high-pressure fuel tanks 12A and 12B so that it is equal to or greater than the remaining amount threshold. Furthermore, the control circuit 90 increases the internal pressure of either the high-pressure fuel tank 12A or 12B that supplies liquefied hydrogen to the internal combustion engine E to the second set pressure P2. 【0086】 In steps S114 to S124, the control circuit 90 controls the compressor 30 to maintain the pressure of the hydrogen gas supplied to the internal combustion engine E from the high-pressure fuel tank 12A or 12B that supplies liquefied hydrogen at a first set pressure P1. When the remaining amount of liquefied hydrogen in the high-pressure fuel tank 12A or 12B falls below the remaining amount threshold, the control circuit switches the high-pressure fuel tank supplying liquefied hydrogen to the other high-pressure fuel tank 12B or 12A to maintain the supply of hydrogen gas to the internal combustion engine E, while replenishing the high-pressure fuel tank 12A or 12B with liquefied hydrogen. 【0087】In steps S114 to S125, the control circuit 90 terminates fuel supply control in accordance with a command from the driver, but the termination of fuel supply control is not limited to this. For example, the control circuit 90 may terminate fuel supply control when the amount of liquefied hydrogen remaining in the low-pressure fuel tank 11 falls below a predetermined amount. The control circuit 90 may also terminate fuel supply control when an abnormality in the internal combustion engine E or an abnormality in a component of the fuel supply system 100 is detected. 【0088】 In steps S114 to S125, the control circuit 90 may continue or temporarily stop the operation of the compressor 30. For example, the control circuit 90 may continue the operation of the compressor 30 while the consumption of hydrogen gas by the internal combustion engine E continues. The control circuit 90 may stop the operation of the compressor 30 if the internal pressure of at least one of the fuel tanks 11, 12A, and 12B is sufficiently high, until the internal pressure of the fuel tank with the sufficiently high internal pressure drops to the desired internal pressure. An example of a fuel tank with sufficiently high internal pressure may include the internal pressure of the low-pressure side fuel tank 11 being greater than the third set pressure P3, and the internal pressure of the high-pressure side fuel tanks 12A and 12B being greater than the second set pressure P2. An example of a fuel tank with a desired internal pressure may include the internal pressure of the low-pressure side fuel tank 11 being the third set pressure P3, and the internal pressure of the high-pressure side fuel tanks 12A and 12B being the second set pressure P2. 【0089】In controlling the compressor 30 in steps S115 and S119, the control circuit 90 may increase the output of the compressor 30 so that the discharge rate increases as the amount of hydrogen gas consumed by the internal combustion engine E increases. The consumption rate and discharge rate may be amounts per unit time. The control circuit 90 may also control the output of the compressor 30 to increase or decrease the discharge rate based on information about the mobile body provided from the mobile body's electronic control unit. The mobile body information may be a command input by the driver requesting an increase in the output of the internal combustion engine E to accelerate the mobile body. This allows the control circuit 90 to increase the discharge rate of the compressor 30 and raise the internal pressure of the high-pressure fuel tanks 12A and 12B before the amount of hydrogen gas consumed by the internal combustion engine E actually increases due to the increase in output. Thus, it is possible to prevent a shortage of hydrogen gas supplied to the internal combustion engine E. 【0090】 In this embodiment, the compressor 30 is implemented as an electric compressor, and the compressor 30 can operate independently of the internal combustion engine E. Therefore, the control circuit 90 can operate and stop the compressor 30 independently of the operation of the internal combustion engine E. The control circuit 90 may be configured to stop the operation of the compressor 30 in situations where pressurization of hydrogen gas by the compressor 30 is unnecessary, such as when the amount of hydrogen gas consumed by the internal combustion engine E is small. This reduces energy consumption caused by the operation of the compressor 30 in the mobile unit. 【0091】 Modification 1 of the embodiment will now be described. Modification 1 differs from the embodiment in that the fuel supply system is equipped with a single fuel tank. In the following, the differences between Modification 1 and the embodiment will be explained, and explanations of points that are the same as in the embodiment will be omitted as appropriate. 【0092】Figure 4 shows an example of the configuration of a fuel supply system 101 according to Modification 1. As shown in Figure 4, the fuel supply system 101 includes one fuel tank 10, compared to the fuel supply system 100 according to the embodiment. The fuel supply system 101 includes components related to the first high-pressure side fuel tank 12A according to the embodiment, but does not include components related to the second high-pressure side fuel tank 12B or the low-pressure side fuel tank 11 according to the embodiment. The fuel supply system 101 includes the fuel tank 10 using a configuration similar to the configuration including the first high-pressure side fuel tank 12A according to the embodiment. The fuel tank 10 has the same liquid fuel capacity as the low-pressure side fuel tank 11 according to the embodiment, and has the same pressure resistance as the high-pressure side fuel tanks 12A and 12B according to the embodiment. 【0093】 The fuel supply system 101 includes a fuel tank 10, a vaporizer 20, a pre-vaporization passage 42, a post-vaporization passage 50, an injection pressure control valve 51, a return passage 60, a compressor 30, a compressor pressure control valve 31, a bypass passage 60a, and a control circuit 90. 【0094】 The pre-vaporization flow path 42 is the same as the combination of the first downstream pre-vaporization flow path 42A and the vaporizer-side merging flow path 42C according to the embodiment. The return flow path 60 is the same as the combination of the first return flow path 60A and the vaporizer-side common flow path 60C according to the embodiment. The bypass flow path 60a is the same as the bypass flow path 60Ca according to the embodiment. 【0095】 The fuel tank 10 is equipped with a safety valve 10a, similar to the safety valve 11a of the low-pressure fuel tank 11 according to the embodiment. The safety valve 10a maintains the internal pressure of the fuel tank 10 at or below a preset fifth set pressure P5. The fifth set pressure P5 may be set from a range greater than the second set pressure P2 and less than or equal to the pressure resistance of the fuel tank 10. The fuel tank 10 includes a temperature sensor, a pressure sensor, and a liquid level sensor, similar to the low-pressure fuel tank 11 according to the embodiment. 【0096】In the fuel supply system 101 according to Modification 1, the fuel gas in the return passage 60 is pressurized to a second set pressure P2 by the compressor 30, and the fuel gas at the second set pressure P2 is filled into the fuel tank 10. As a result, the internal pressure of the fuel tank 10 is maintained at the second set pressure P2. The liquid fuel in the fuel tank 10 is sent to the pre-vaporization passage 42 by this fuel gas and vaporized into fuel gas by the vaporizer 20. The fuel gas is reduced in pressure to a first set pressure P1 by the injection pressure control valve 51 and sent to the internal combustion engine E and the return passage 60. Because the second set pressure P2 is higher than the first set pressure P1, the fuel gas after reduction by the injection pressure control valve 51 can maintain the pressure of the first set pressure P1 regardless of the increase or decrease in fuel consumption in the internal combustion engine E. 【0097】 Modification 2 of the embodiment will now be described. Modification 2 differs from the embodiment in that the high-pressure fuel tank is housed inside the low-pressure fuel tank of the fuel supply system. In the following, the differences between Modification 2 and the embodiment and Modification 1 will be described, and explanations of points that are the same as in the embodiment or Modification 1 will be omitted as appropriate. 【0098】 Figure 5 shows an example of the configuration of a fuel supply system 102 according to Modification 2. As shown in Figure 5, the fuel supply system 102 has the same components as the fuel supply system 100 according to the embodiment. The fuel supply system 102 includes high-pressure fuel tanks 12A and 12B inside the low-pressure fuel tank 11. In this modification, the high-pressure fuel tanks 12A and 12B are located at the bottom of the low-pressure fuel tank 11. The upstream pre-vaporization passages 41A and 41B each extend from the high-pressure fuel tanks 12A and 12B into the interior of the low-pressure fuel tank 11 and open. For example, the upstream pre-vaporization passages 41A and 41B may open near the bottom of the low-pressure fuel tank 11 so that liquid fuel can be stably taken in. The upstream check valves 43A and 43B of the upstream pre-vaporization passages 41A and 41B are located inside the low-pressure fuel tank 11. 【0099】The downstream pre-vaporization passages 42A, 42B, the return passages 60A, 60B, and the gas filling passage 70 extend from the inside to the outside of the low-pressure fuel tank 11. In this modified example, the downstream check valves 44A, 44B are located inside the low-pressure fuel tank 11, but they may be located on the outer shell or outside of the low-pressure fuel tank 11. The solenoid valves, the switching valves 61A, 61B, are preferably located outside the low-pressure fuel tank 11. The gas filling pressure control valve 71 is located outside the low-pressure fuel tank 11, but it may be located inside. 【0100】 The discharge passages 12Aa and 12Ba extend from the inside to the outside of the low-pressure fuel tank 11. The on / off control valves 12Ab and 12Bb, which are solenoid valves, are preferably located outside the low-pressure fuel tank 11. The compressor 30, compressor pressure control valve 31, vaporizer 20, and injection pressure control valve 51 are located outside the low-pressure fuel tank 11. The fuel supply system 102 is equipped with various sensors similar to those in the fuel supply system 100 according to this embodiment. 【0101】 According to the fuel supply system 102 of Modified Example 2, since the high-pressure fuel tanks 12A and 12B are located inside the low-pressure fuel tank 11, the ambient temperature around the high-pressure fuel tanks 12A and 12B stabilizes at the temperature of the liquid fuel. This eliminates the need for a structure to insulate the high-pressure fuel tanks 12A and 12B. Furthermore, the piping connecting the high-pressure fuel tanks 12A and 12B and the low-pressure fuel tank 11 is simplified and reduced in volume. 【0102】 While exemplary embodiments and modifications of the present disclosure have been described above, the present disclosure is not limited to the above embodiments and modifications. That is, various modifications and improvements are possible within the scope of the present disclosure. For example, various modifications applied to embodiments or modifications, and forms constructed by combining components from different embodiments and modifications, are also included within the scope of the present disclosure. 【0103】For example, the mobile body on which the fuel supply system according to the embodiment and its modifications is installed may be a manned vehicle or an unmanned vehicle. The mobile body may comprise the fuel supply system, a fuel consumption source E, a propulsion device for propelling the mobile body, a power transmission mechanism for transmitting the energy generated by the fuel consumption source E to the propulsion device, and an electronic control unit. The propulsion device may be wheels. Examples of such mobile bodies may include two-wheeled vehicles, three-wheeled vehicles, four-wheeled vehicles, and railway vehicles. The mobile body may be a ship or an aircraft. In this case, the propulsion device may be a propeller or a fan. The electronic control unit, also called an ECU, controls the entire mobile body. For example, the electronic control unit controls the fuel consumption source E and the fuel supply system according to signals received from the operator. 【0104】 In the embodiments and modifications, the fuel is hydrogen, but is not limited to hydrogen. The fuel may be a gaseous fuel at room temperature and pressure. Examples of such fuels include, in addition to hydrogen, methane, ethane, propane, and carbon-hydrogen gases such as acetylene gas. Furthermore, the fuel may be a fuel that is liquefied by cooling or compression and treated as a liquid fuel. 【0105】 In embodiments and modifications, the fuel consumption source E is an internal combustion engine, but is not limited thereto. For example, examples of fuel consumption source E may include fuel cells and boilers. The fuel consumption source E can preferably be used in a system that supplies vaporized fuel at a pressure higher than atmospheric pressure, specifically at a pressure of 1 megapascal or more, to the fuel consumption source. 【0106】 In the embodiments and modifications, the compressor 30 is an electric compressor driven by an electric actuator, but the structure of the compressor 30 is not limited thereto. For example, the compressor 30 may be a mechanical compressor driven by the mechanical energy output of an internal combustion engine E. For example, the compressor 30 may be connected to the crankshaft via a power transmission member such as a belt so that the rotational power of the crankshaft of the internal combustion engine E is transmitted to it. Such a compressor 30 may be a rotary compressor that includes a rotor that rotates due to the rotational power transmitted from the crankshaft. 【0107】In the embodiments and modifications, the high-pressure fuel tanks 12A, 12B and the low-pressure fuel tank 11 are configured to directly press the liquid fuel with gas, but are not limited thereto. For example, the high-pressure fuel tanks 12A, 12B and the low-pressure fuel tank 11 may include a partition wall, such as a piston, that is slidable between the gas region and the liquid fuel region, and have a structure in which the partition wall is pressed and moved by the fuel gas. In the high-pressure fuel tanks 12A, 12B and the low-pressure fuel tank 11, the liquid fuel may be indirectly pressed with fuel gas. 【0108】 In the embodiments and modifications, the low-pressure fuel tank 11 is equipped with a safety valve 11a, but the high-pressure fuel tanks 12A and 12B may also be equipped with safety valves similar to the safety valve 11a. In this case, the safety valves of the high-pressure fuel tanks 12A and 12B may be valves that maintain the internal pressure of the high-pressure fuel tanks 12A and 12B at or below a set pressure set higher than the second set pressure P2. The safety valve may also be a relief valve that releases pressure exceeding the set pressure. 【0109】 The fuel supply system according to the embodiment and modified examples may include on-off control valves interposed in the upstream pre-vaporization passages 41A and 41B, respectively, which operate to open and close the upstream pre-vaporization passages 41A and 41B. The on-off control valves may be solenoid valves, similar to the switching valves 61A and 61B. The control circuit 90 may also control the on-off control units of the upstream pre-vaporization passages 41A and 41B to a closed state when the compressor 30 is stopped. This prevents liquid fuel in the low-pressure fuel tank 11 from leaking into the high-pressure fuel tanks 12A and 12B when the fuel consumption source E and the compressor 30 are stopped. 【0110】The fuel supply system according to the embodiment and its modifications may include an accumulator in the flow path downstream of the compressor 30. The accumulator stores the pressure of the fluid, that is, it stores the pressure energy of the fluid. For example, the accumulator may be located in the common flow path 60C on the vaporizer side. In this way, the accumulator stores the pressure energy of the fuel gas produced in the compressor 30. When the pressure of the fuel gas in the common flow path 60C on the vaporizer side decreases, the accumulator can compensate for the pressure drop by releasing the pressure energy. Therefore, even if the amount of liquid fuel remaining in the high-pressure fuel tanks 12A and 12B and the low-pressure fuel tank 11 decreases sharply due to a rapid increase in fuel consumption by the fuel consumption source E, the release of pressure energy from the accumulator makes it easier to compensate for the shortage of fuel supply to the fuel consumption source E. 【0111】 The fuel supply system according to the embodiment and its modifications may be equipped with a safety valve similar to the safety valve 11a of the low-pressure fuel tank 11 in the passage that has the highest pressure in the passage. For example, such a safety valve may be placed in one or more of the first downstream pre-vaporization passage 42A, the second downstream pre-vaporization passage 42B, and the vaporizer-side merging passage 42C. The safety valve may also be a relief valve that releases pressure exceeding a set pressure. 【0112】 In the embodiments and modifications, the upstream pre-vaporization passage 41 includes a low-pressure tank-side common passage 41C and two upstream pre-vaporization passages 41A and 41B that branch off from the low-pressure tank-side common passage 41C, but it does not have to include the low-pressure tank-side common passage 41C. In this case, the upstream pre-vaporization passages 41A and 41B may each be independently connected to the low-pressure fuel tank 11. 【0113】 In the embodiments and modifications, the downstream pre-vaporization flow path 42 includes separately extending downstream pre-vaporization flow paths 42A and 42B, and a vaporizer-side confluence flow path 42C into which the downstream pre-vaporization flow paths 42A and 42B merge. However, the vaporizer-side confluence flow path 42C may be omitted. In this case, the downstream pre-vaporization flow paths 42A and 42B may be independently connected to the vaporizer 20. 【0114】In the embodiment and modified examples, the return passage 60 is connected to the portion of the post-vaporization passage 50 downstream of the injection pressure control valve 51, that is, the portion between the injection pressure control valve 51 and the fuel consumption source E. However, it may also be connected to the portion of the post-vaporization passage 50 upstream of the injection pressure control valve 51. In this case, the fuel gas before depressurization by the injection pressure control valve 51 flows into the return passage 60. As a result, the compressor 30 compresses the fuel gas at a higher pressure, which can reduce the energy consumption of the compressor 30. 【0115】 In the embodiments and modifications, the low-pressure fuel tank 11 has a structure that receives fuel gas pressurized by the compressor 30 via the gas filling passage 70 and pushes the liquid fuel in the low-pressure fuel tank 11 to the outside with the filled fuel gas, but the structure of the low-pressure fuel tank 11 is not limited thereto. For example, the filling of the low-pressure fuel tank 11 with fuel gas may be performed by components other than the compressor 30. For example, the fuel supply system may include the compressor 30 to send fuel gas to the high-pressure fuel tanks 12A and 12B, and further include another compressor to send fuel gas to the low-pressure fuel tank 11. This allows the control circuit 90 to perform control over the low-pressure fuel tank 11 independently of the control over the high-pressure fuel tanks 12A and 12B. 【0116】 For example, the gas filling passage 70 may connect the passage upstream of the compressor 30 in the direction of fuel gas flow to the low-pressure fuel tank 11. In this case, the gas filling passage 70 may be connected to the vaporizer-side common passage 60C or to the post-vaporization passage 50. As a result, the pressure of the fuel gas flowing through the gas filling passage 70 may be lower than the pressure of the fuel gas in the return passages 60A and 60B downstream of the compressor 30. The low-pressure fuel tank 11 may be filled with fuel gas at a lower pressure than that in the high-pressure fuel tanks 12A and 12B. 【0117】For example, the gas filled in the low-pressure fuel tank 11 may be a gas other than fuel gas. Such a gas is preferably one with low reactivity with liquid fuel. For example, the gas filled in the low-pressure fuel tank 11 may be atmospheric air. The gas filled in the low-pressure fuel tank 11 may be supplied to the gas filling passage 70 from outside the fuel supply system. 【0118】 For example, the fuel supply system may include a heater for heating the gas that fills the low-pressure fuel tank 11. An example of a heater may be an electric heater. The heater may be located either inside or outside the low-pressure fuel tank 11. When the amount of fuel gas consumed by the fuel consumption source E is small, the control circuit 90 may use the heater to heat the gas that fills the low-pressure fuel tank 11, thereby vaporizing the liquid fuel stored in the low-pressure fuel tank 11. The fuel gas vaporized from the liquid fuel increases the internal pressure of the low-pressure fuel tank 11, thereby pushing out the liquid fuel in the low-pressure fuel tank 11. 【0119】 Therefore, the fuel supply system only needs to be able to increase the amount of gas in the low-pressure fuel tank 11. For this reason, the fuel supply system does not need to include a gas filling passage 70. Even if the fuel supply system includes a gas filling passage 70, the gas filling passage 70 does not need to be in communication with the return passage 60. 【0120】In the embodiments and modifications, the control circuit 90 calculates the remaining amount of liquid fuel in each of the high-pressure fuel tanks 12A, 12B and the low-pressure fuel tank 11 using the detection results of the liquid level sensors contained in each of the high-pressure fuel tanks 12A, 12B and the low-pressure fuel tank 11, but the remaining amount of liquid fuel may be estimated by other methods. For example, the control circuit 90 may obtain information on the amount of fuel injected from the fuel injector of the internal combustion engine E from the electrical control unit of the mobile body. The control circuit 90 may calculate the remaining amount of liquid fuel in the low-pressure fuel tank 11 based on the cumulative value of the fuel injection amount. The control circuit 90 may calculate the remaining amount of liquid fuel in the first high-pressure fuel tank 12A based on the cumulative value of the fuel injection amount during the period when the first switching valve 61A is open. The control circuit 90 may calculate the remaining amount of liquid fuel in the second high-pressure fuel tank 12B based on the cumulative value of the fuel injection amount during the period when the second switching valve 61B is open. 【0121】 For example, the fuel supply system may include flow sensors in the flow path through which the liquid fuel flows. The control circuit 90 may calculate the remaining amount of liquid fuel in the low-pressure fuel tank 11 based on the detection result of the flow sensor located in the low-pressure tank side common flow path 41C, or the detection results of the flow sensors located in the upstream pre-vaporization flow paths 41A and 41B, respectively. The control circuit 90 may calculate the remaining amount of liquid fuel in the first high-pressure fuel tank 12A based on the detection result of the flow sensor located in the first downstream pre-vaporization flow path 42A, or the detection results of the flow sensors located in the first downstream pre-vaporization flow path 42A and the first upstream pre-vaporization flow path 41A, respectively. The control circuit 90 may calculate the remaining amount of liquid fuel in the second high-pressure fuel tank 12B based on the detection result of the flow sensor located in the second downstream pre-vaporization flow path 42B, or the detection results of the flow sensors located in the second downstream pre-vaporization flow path 42B and the second upstream pre-vaporization flow path 41B, respectively. 【0122】In the embodiments and modified examples, the gas filling switching valve 61 switches between the high-pressure fuel tank 12A or 12B to which fuel gas should be supplied by the operation of two switching valves 61A and 61B, but the configuration of the gas filling switching valve 61 is not limited thereto. For example, the gas filling switching valve 61 may be a three-way valve interposed at the connection between the first return passage 60A and the second return passage 60B. In this case, the three-way valve may switch between two states. One state is one in which the first return passage 60A and the vaporizer-side common passage 60C are connected, and communication between the second return passage 60B and the vaporizer-side common passage 60C is blocked. The other state is one in which the second return passage 60B and the vaporizer-side common passage 60C are connected, and communication between the first return passage 60A and the vaporizer-side common passage 60C is blocked. 【0123】 In the embodiments and modifications, the fuel supply system includes two high-pressure fuel tanks 12A and 12B, but it may also include three or more high-pressure fuel tanks. The fuel supply system includes one low-pressure fuel tank 11, but it may also include two or more low-pressure fuel tanks. For example, the gas filling switching valve 61 may have a structure that switches the flow path to send fuel gas to one or more of the three or more high-pressure fuel tanks. For example, under normal conditions, the control circuit 90 may operate the gas filling switching valve 61 to send fuel gas to one high-pressure fuel tank. This causes liquid fuel to be discharged from one high-pressure fuel tank. If the amount of fuel gas to be supplied to the fuel consumption source E temporarily increases, the control circuit 90 may operate the gas filling switching valve 61 to send fuel gas to two or more high-pressure fuel tanks. This allows liquid fuel to be discharged from two or more high-pressure fuel tanks simultaneously. 【0124】In the embodiments and modifications, the fuel supply system comprises one compressor 30, but is not limited to this, and may comprise two or more compressors 30. For example, the fuel supply system may comprise multiple compressors 30 corresponding to the number of high-pressure fuel tanks. For example, the fuel supply system may comprise a compressor 30 for each high-pressure fuel tank, and each compressor 30 may be configured to pressurize the fuel gas sent to the high-pressure fuel tank corresponding to the compressor 30. For example, the fuel supply system may comprise a compressor 30 for the low-pressure fuel tank 11. In the embodiments and modifications, the fuel supply system comprises one vaporizer 20, but is not limited to this, and may comprise two or more vaporizers 20. For example, the fuel supply system may comprise multiple vaporizers 20 corresponding to the number of high-pressure fuel tanks. For example, the fuel supply system may comprise a vaporizer 20 for each high-pressure fuel tank, and each vaporizer 20 may be configured to vaporize the liquid fuel sent from the high-pressure fuel tank corresponding to the vaporizer 20. 【0125】 Examples of each aspect of the present disclosure will now be described. A fuel supply system according to the first aspect of the present disclosure comprises a fuel tank for storing liquid fuel, a vaporizer for vaporizing the liquid fuel into fuel gas, a pre-vaporization passage connecting the fuel tank and the vaporizer, a post-vaporization passage connecting the vaporizer and a fuel consumption source, a return passage connecting the post-vaporization passage and the fuel tank, and a compressor interposed in the return passage for compressing the fuel gas flowing through the post-vaporization passage and filling the fuel tank with the compressed fuel gas. 【0126】 According to the first embodiment, compressed fuel gas is filled into the fuel tank by a compressor. This maintains a high pressure state inside the fuel tank. Even if fuel consumption by the fuel source increases sharply, it is easy to maintain a high pressure state inside the fuel tank. This ensures that the internal pressure of the tank necessary for fuel supply is maintained, preventing fuel shortages. Furthermore, by filling the fuel tank with fuel gas to guide the liquid fuel to the vaporizer, mechanical structures such as propellers that come into contact with the liquid fuel and guide it to the vaporizer become unnecessary, thereby increasing the durability of the fuel supply system. 【0127】In a fuel supply system according to the first embodiment, a fuel supply system according to the second embodiment of the present disclosure further comprises a control valve interposed in the post-vaporization flow path for reducing the fuel gas vaporized by the vaporizer to a pressure suitable for supply to the fuel consumption source, and the return flow path may be configured to be connected to the post-vaporization flow path downstream of the control valve. 【0128】 According to the second embodiment, the fuel gas after pressure adjustment can be compressed by a compressor, making it easier to prevent fluctuations in the pressure of the fuel gas being filled. 【0129】 In a fuel supply system according to the first or second aspect, the fuel supply system according to the third aspect of the present disclosure includes a fuel tank comprising a low-pressure fuel tank and a high-pressure fuel tank, the pre-vaporization passage comprising an upstream pre-vaporization passage connecting the low-pressure fuel tank and the high-pressure fuel tank, and a downstream pre-vaporization passage connecting the high-pressure fuel tank and the vaporizer, the return passage comprising a post-vaporization passage and the high-pressure fuel tank, and the fuel supply system further comprising a first check valve interposed in the upstream pre-vaporization passage to prevent backflow from the high-pressure fuel tank to the low-pressure fuel tank. 【0130】 According to the third embodiment, by dividing the fuel tank into a high-pressure fuel tank and a low-pressure fuel tank, a structure suitable for each function can be adopted, increasing the degree of design freedom. In addition, the provision of a first check valve prevents fuel from flowing back from the high-pressure fuel tank to the low-pressure fuel tank. 【0131】 In a fuel supply system according to a third embodiment, the fuel supply system according to a fourth embodiment of the present disclosure may be configured such that the capacity of the low-pressure fuel tank is greater than the capacity of the high-pressure fuel tank. 【0132】 According to the fourth embodiment, increasing the capacity of the low-pressure fuel tank reduces the frequency of fuel refilling or fuel tank replacement. Furthermore, reducing the capacity of the high-pressure fuel tank makes it easier to realize a structure for the high-pressure fuel tank that can withstand the filling of fuel gas compressed by the compressor. 【0133】In a fuel supply system according to a fourth embodiment, the fuel supply system according to a fifth embodiment of the present disclosure may be configured such that the low-pressure fuel tank houses the high-pressure fuel tank. 【0134】 According to the fifth embodiment, temperature changes in the high-pressure fuel tank can be suppressed, and the supply of liquid fuel can be stabilized. 【0135】 In a fuel supply system according to a fourth or fifth embodiment, the fuel supply system according to a sixth embodiment of the present disclosure may further include a gas filling passage that supplies a filling gas to the low-pressure fuel tank at a pressure lower than the pressure of the fuel gas supplied to the high-pressure fuel tank. 【0136】 According to the sixth embodiment, filling the low-pressure fuel tank with filling gas from the gas filling passage facilitates the movement of liquid fuel from the low-pressure fuel tank to the high-pressure fuel tank. 【0137】 In a fuel supply system according to the sixth aspect, the fuel supply system according to the seventh aspect of the present disclosure may be configured such that the gas filling passage connects the post-vaporization passage and the low-pressure side fuel tank, and the fuel supply system further comprises a filling pressure reducing valve interposed in the gas filling passage for reducing the pressure of the fuel gas to a pressure lower than the pressure of the fuel gas sent to the high-pressure side fuel tank and higher than atmospheric pressure. 【0138】 According to the seventh embodiment, the fuel gas flowing through the existing post-vaporization flow path can be used as the filling gas to fill the low-pressure fuel tank. This makes it easier to simplify the structure for gas filling compared to when a gas other than fuel gas is used to fill the low-pressure fuel tank. 【0139】 In a fuel supply system according to any one of the third to seventh embodiments, the fuel supply system according to the eighth embodiment of the present disclosure may further include a second check valve interposed in the downstream pre-vaporization flow path to prevent backflow from the vaporizer toward the high-pressure fuel tank. 【0140】According to the eighth embodiment, a second check valve is provided in the downstream pre-vaporization flow path, which prevents liquid fuel from flowing back from the vaporizer side into the high-pressure fuel tank when the internal pressure of the high-pressure fuel tank fluctuates. 【0141】 In a fuel supply system according to any one of the third to eighth embodiments, in the fuel supply system according to the ninth embodiment of the present disclosure, a plurality of high-pressure fuel tanks are provided, and the fuel supply system may further include a gas filling switching valve interposed in the return passage for switching among the plurality of high-pressure fuel tanks which should supply the fuel gas compressed by the compressor. 【0142】 According to the ninth embodiment, the high-pressure fuel tank to be filled with fuel gas can be switched using a switching valve. This makes it possible to reduce the number of compressors to less than the number of high-pressure fuel tanks, and thus simplify the structure of the fuel supply system. 【0143】 In a fuel supply system according to any one of the third to ninth embodiments, the fuel supply system according to the tenth embodiment of the present disclosure may further include a plurality of high-pressure fuel tanks, and the fuel supply system may further include one or more discharge passages for discharging gas from the plurality of high-pressure fuel tanks, and one or more gas discharge valves interposed in the one or more discharge passages for switching among the plurality of high-pressure fuel tanks which high-pressure fuel tanks should discharge the gas contained within. 【0144】 According to the tenth embodiment, the internal pressure of multiple high-pressure fuel tanks can be selectively reduced by switching with one or more gas discharge valves, thereby promoting fuel supply from the low-pressure fuel tank to the high-pressure fuel tank. 【0145】A fuel consumption source system according to an eleventh aspect of the present disclosure comprises a fuel consumption source that is driven by being supplied with fuel gas as fuel, a low-pressure fuel tank and a high-pressure fuel tank that store liquid fuel obtained by liquefying the fuel gas, a vaporizer that vaporizes the liquid fuel into the fuel gas, an upstream pre-vaporization passage connecting the low-pressure fuel tank and the high-pressure fuel tank, a downstream pre-vaporization passage connecting the high-pressure fuel tank and the vaporizer, a post-vaporization passage connecting the vaporizer and the fuel consumption source, a return passage connecting the post-vaporization passage to the high-pressure fuel tank and the low-pressure fuel tank, and a pressure control valve that raises the pressure of the high-pressure fuel tank to a level higher than the pressure of the low-pressure fuel tank, wherein the capacity of the high-pressure fuel tank is smaller than the capacity of the low-pressure fuel tank. 【0146】 According to the eleventh embodiment, since the capacity of the high-pressure fuel tank is smaller than the capacity of the low-pressure fuel tank, it is easier to quickly raise the internal pressure of the high-pressure fuel tank to a high-pressure state when starting up the fuel consumption source, compared to when the low-pressure fuel tank is pressurized, and thus prevent fuel supply shortages. 【0147】 A fuel supply method according to a twelfth aspect of the present disclosure includes: supplying liquid fuel to a plurality of high-pressure fuel tanks; filling a first high-pressure fuel tank among the plurality of high-pressure fuel tanks with compressed gas from a compressor and supplying vaporized fuel from the first high-pressure fuel tank to a fuel consumption source via a vaporizer; determining whether the amount of liquid fuel stored in the first high-pressure fuel tank is below a threshold; if it is determined that the amount of liquid fuel stored in the first high-pressure fuel tank is below the threshold, filling a second high-pressure fuel tank among the plurality of high-pressure fuel tanks with compressed gas from the compressor and supplying vaporized fuel from the second high-pressure fuel tank to the fuel consumption source via the vaporizer or another vaporizer; and if it is determined that the amount of liquid fuel stored in the first high-pressure fuel tank is below the threshold, opening the gas discharge passage of the first high-pressure fuel tank to discharge the contained gas and supplying liquid fuel to the first high-pressure fuel tank. 【0148】According to the twelfth embodiment, when the amount of liquid fuel stored in the first high-pressure fuel tank decreases, the internal pressure of the first high-pressure fuel tank is lowered. This enables a smooth supply of liquid fuel to the first high-pressure fuel tank. While liquid fuel is being supplied to the first high-pressure fuel tank, the fuel in the second high-pressure fuel tank is supplied to the fuel consumption source. Therefore, the liquid fuel filling operation to the high-pressure fuel tank can be performed while maintaining the fuel supply state to the fuel consumption source. As a result, fuel supply shortages caused by the supply of fuel to the high-pressure fuel tank can be suppressed. 【0149】The functions of the elements disclosed herein may be implemented using one or more circuits or processing circuits, including general-purpose processors, special-purpose processors, integrated circuits, ASICs (Application Specific Integrated Circuits), FPGAs (Field Programmable Gate Arrays), and / or conventional circuits. The functions of the elements disclosed herein may be implemented using one or more circuits or processing circuits, including a combination of general-purpose processors, special-purpose processors, integrated circuits, ASICs, FPGAs, and conventional circuits. One or more circuits or processing circuits may be programmed using one or more programs stored together or individually in one or more memories, or may be otherwise configured to perform the disclosed functions. A processor is considered a processing circuit or circuit because it includes transistors and other circuits. A processor may be a programmed processor that executes programs stored in memory. In this disclosure, a circuit, unit, or means is hardware that performs the enumerated functions individually or in combination with each other, or hardware programmed to perform the enumerated functions individually or in combination with each other. The hardware may be any hardware disclosed herein that is programmed or configured to perform the enumerated functions. The computer program, including computer instructions, is stored in memory. The computer instructions provide logic and routines that enable the hardware to perform the methods disclosed herein. The hardware includes, for example, processing circuits or circuits. The computer program may be implemented in a known format on computer-readable storage media, computer program products, memory devices, recording media such as CD-ROMs or DVDs, and / or in the memory of FPGAs or ASICs. 【0150】All ordinal numbers, quantities, and other figures used herein are illustrative to illustrate the technology of this disclosure, and this disclosure is not limited to such illustrative figures. The connections between components are illustrative to illustrate the technology of this disclosure, and the connections that realize the functions of this disclosure are not limited to these. 【0151】 This disclosure can be implemented in various ways without departing from the scope of its essential features, and the scope of this disclosure is defined more by the appended claims than by the description in the specification; therefore, exemplary embodiments and modifications are illustrative and not limiting. All modifications within the claims and their scope, or equivalents within the claims and their scope, are intended to be encompassed by the claims. 【0152】 10 Fuel tank 11 Low-pressure fuel tank 12A, 12B High-pressure fuel tank 12Aa, 12Ba Discharge passage 12Ab, 12Bb On / off control valve (gas discharge valve) 20 Vaporizer 30 Compressor 40 Pre-vaporization passage 41, 41A, 41B Upstream pre-vaporization passage 42, 42A, 42B Downstream pre-vaporization passage 43A, 43B Upstream check valve (first check valve) 44A, 44B Downstream check valve (second check valve) 50 Post-vaporization passage 51 Injection pressure control valve (regulating valve) 60, 60A, 60B Return passage 61 Gas filling switching valve 61A, 61B Switching valve 70 Gas filling passage 71 Gas filling pressure control valve (reducing pressure valve for filling) 100, 101, 102 Fuel supply system 1000 Fuel consumption source system E Fuel consumption source, internal combustion engine

Claims

1. A fuel supply system comprising: a fuel tank for storing liquid fuel; a vaporizer for vaporizing the liquid fuel into fuel gas; a pre-vaporization passage connecting the fuel tank and the vaporizer; a post-vaporization passage connecting the vaporizer and a fuel consumption source; a return passage connecting the post-vaporization passage and the fuel tank; and a compressor interposed in the return passage for compressing the fuel gas flowing through the post-vaporization passage and filling the fuel tank with the compressed fuel gas.

2. The fuel supply system according to claim 1, further comprising a control valve interposed in the post-vaporization flow path for reducing the pressure of the fuel gas vaporized by the vaporizer to a pressure suitable for supply to the fuel consumption source, wherein the return flow path is connected to the post-vaporization flow path downstream of the control valve.

3. The fuel tank includes a low-pressure fuel tank and a high-pressure fuel tank; the pre-vaporization passage includes an upstream pre-vaporization passage connecting the low-pressure fuel tank and the high-pressure fuel tank, and a downstream pre-vaporization passage connecting the high-pressure fuel tank and the vaporizer; the return passage connects the post-vaporization passage and the high-pressure fuel tank; and the fuel supply system further comprises a first check valve interposed in the upstream pre-vaporization passage to prevent backflow from the high-pressure fuel tank to the low-pressure fuel tank, according to claim 1 or 2.

4. The fuel supply system according to claim 3, wherein the capacity of the low-pressure fuel tank is greater than the capacity of the high-pressure fuel tank.

5. The fuel supply system according to claim 4, wherein the low-pressure fuel tank houses the high-pressure fuel tank.

6. The fuel supply system according to claim 4, further comprising a gas filling channel that supplies a filling gas at a pressure lower than the pressure of the fuel gas supplied to the high-pressure fuel tank to the low-pressure fuel tank.

7. The fuel supply system according to claim 6, wherein the gas filling passage connects the post-vaporization passage and the low-pressure fuel tank, and the fuel supply system further comprises a filling pressure reducing valve interposed in the gas filling passage for reducing the pressure of the fuel gas to a pressure lower than the pressure of the fuel gas sent to the high-pressure fuel tank but higher than atmospheric pressure.

8. The fuel supply system according to claim 3, further comprising a second check valve interposed in the downstream pre-vaporization flow path to prevent backflow from the vaporizer toward the high-pressure fuel tank.

9. The fuel supply system according to claim 3, wherein a plurality of high-pressure fuel tanks are provided, and the fuel supply system further comprises a gas filling switching valve interposed in the return passage for switching among the plurality of high-pressure fuel tanks which should supply the fuel gas compressed by the compressor.

10. The fuel supply system according to claim 3, wherein a plurality of high-pressure fuel tanks are provided, and the fuel supply system further comprises: at least one discharge passage for discharging gas from the plurality of high-pressure fuel tanks, and at least one gas discharge valve interposed in the at least one discharge passage for switching among the plurality of high-pressure fuel tanks which high-pressure fuel tank should discharge the gas contained within.

11. A fuel consumption source system comprising: a fuel consumption source that is driven by being supplied with fuel gas as fuel; a low-pressure fuel tank and a high-pressure fuel tank that store liquid fuel obtained by liquefying the fuel gas; a vaporizer that vaporizes the liquid fuel into the fuel gas; an upstream pre-vaporization passage connecting the low-pressure fuel tank and the high-pressure fuel tank; a downstream pre-vaporization passage connecting the high-pressure fuel tank and the vaporizer; a post-vaporization passage connecting the vaporizer and the fuel consumption source; a return passage connecting the post-vaporization passage to the high-pressure fuel tank and the low-pressure fuel tank; and a pressure control valve that raises the pressure of the high-pressure fuel tank to a level higher than the pressure of the low-pressure fuel tank, wherein the capacity of the high-pressure fuel tank is smaller than the capacity of the low-pressure fuel tank.

12. A fuel supply method comprising: supplying liquid fuel to a plurality of high-pressure fuel tanks; filling a first high-pressure fuel tank among the plurality of high-pressure fuel tanks with compressed gas from a compressor and supplying vaporized fuel from the first high-pressure fuel tank to a fuel consumption source via a vaporizer; determining whether the amount of liquid fuel stored in the first high-pressure fuel tank is below a threshold; if it is determined that the amount of liquid fuel stored in the first high-pressure fuel tank is below the threshold, filling a second high-pressure fuel tank among the plurality of high-pressure fuel tanks with compressed gas from the compressor and supplying vaporized fuel from the second high-pressure fuel tank to the fuel consumption source via the vaporizer or another vaporizer; and if it is determined that the amount of liquid fuel stored in the first high-pressure fuel tank is below the threshold, opening the gas discharge passage of the first high-pressure fuel tank to discharge the contained gas and supplying liquid fuel to the first high-pressure fuel tank.

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